The present invention relates to a pneumatic door locking system for maintaining a door of a carrier of goods, such as a truck or railway car, in a latched condition when the carrier is stationary and the prime mover therefor is inoperative or disconnected. More specifically the system is connected to a source of pressurized air operated by the prime mover and is operative when air pressure is supplied thereto, to maintain the door in an unlatched position and when air pressure is vented or disconnected therefrom, to maintain the door in a latched position thereby to prevent theft or pilfering of goods from the carrier.
Heretofore a pneumatically actuated door locking system for a railway car door has been proposed which system is normally locked and which is operable for a limited time with a key only following operation of the air brakes for the car. Such a system is disclosed in U.S. Pat. No. 1,647,225. Also pneumatic door locking systems for automobiles have heretofore been proposed. In this respect a vacuum operated system is disclosed in U.S. Pat. No. 2,888,287 and a motor operated (air pressure operated) door latch system is disclosed in U.S. Pat. No. 1,555,174. The latter system discloses a door latch mechanism which is operable to open a vehicle door when air pressure is supplied thereto and to latch the door when air pressure is vented therefrom. This door latch mechanism functions in a manner similar to the latch mechanism of the door locking system of the present invention hereinafter described in detail. However the construction, operation and function of the door locking system of the present invention differs from the motor operated door latch disclosed in U.S. Pat. No. 1,555,174 as will become apparent from the following description of the door locking system of the present invention.